US2499065A - Device for adjustably positioning spaced magnetic fields - Google Patents

Description

Feb. 28, 1950 M. R. HEPPNER DEVICE FOR ADJUSTABLY POSITIONING SPACED MAGNETIC FIELDS Filed March 22 1949 .2517/272 for.

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fyron Patented Feb. 28, 1950 DEVICE FOR ADJ USTABLY POSITIONING SPACED IWAGNETIOFIELDS Myron R. Heppner, Chicago, 111., assigno'r to Hepp'ner Manufacturing Company, Round Lake, Ill.,'--a corporation of Illinois Application March 22, 1949, SerialNo. 82,813

'6 Claims.

This invention rela'tes'to improvements in a {device ior'pr'eventing the passage of ions to the fluo'rescent surface of "a 'cathoderay tube while permitting the passage of an electron stream to --saidsurface, and refers particularly to a device 'for critically adjusting the'direction of travel'of the electron stream.

It is known that a cathode-ray tube operates on the principle of projecting or discharging a stream of elec'tronsfrom a discharge device into contact with a screen of fluorescent material. It is also known that the discharging of such electron stream is accompanied by the formation of ions which, if brought into contact with the fluorescent material comprising the-screen, are detrimental to the "screen. It is further known that a stream of electrons can be deflected by a magnetic field and that ions have the same characteristics. However, fora magnetic field of predetermined intensity, electrons'and ions do not respond, insofar as deflection is concerned, to the same degree.

This has led to the development in a cathoderay tube of an electron discharge device or gun which projects the stream of electrons at an angle to the axis of the tube; passing the electron stream through a plurality of magnetic fields of different intensities and directions and subsequently passing the streamthrough a relatively small aperture to the fluorescent screen. By subjecting both the electrons and ions to the same magnetic fieldsdeflection of the streams occurs to difierent degrees and, hence, the ion stream does not follow the electron stream through the aperture but is obstructed by the wall in which the aperture is provided.

In my copendin'g application for United States Letters Patent Serial No. 70,053, filed January 10, 1949.1 show and describe a convenient and eflicient means for setting up spaced magnetic fields along the length of'the electron stream, the fields being of different predetermined strength and being in opposite direction,the spaced'fields being adapted to exert forces upon the electron stream such as topermit said stream'to pass through the aperture in the obstructing wall and impinge uponthefluorescent surface while at the same time preventing ions from passing through said aperture.

In my present invention means for setting up spaced'magnetic fields along the length of'the electron stream is contemplated with the improvement comprising conveniently manipulated means for adjustably altering the radial position f the axis of greatest magnetic field intensity '2 of one of saidmagnetic fields with respect'to the axis of the electronstream'.

The objects and advantages of my invention will be apparentfrom' the accompanying drawings and following detaileddescription.

In the drawings:

'Fig. 1 is aside view of a cathode-ray tube, "parts beingbroken away and parts'bein'g shown in section, with my improveddevice' mounted in operative position upon the neck of the tube.

Fig-2 is a fragmentary sectional'view, parts "being shownimelevatiomandparts being broken away of the'neck of thetube, the section being at right angles tothe View illustrated in Fig. 1.

Fig. 3" is a transverse sec'tionalview taken on line-3 3 of Fig. 1.

--Fig.'4 is a View similar to Fig. 3 illustrating the flux shorting ring in a "different 1 position.

Fig. 5 isafront elevational view of my improved device, and

' or face portion 6.

-Within the tube I an electron discharge device l is positioned adjacent the base 2. The function -of the device "I is to project or discharge a stream of electrons and is usually referred to as an electron gun. Adjacent the discharge device I is a member -8 which carries oppositely extending 1 arms '9, the arms being positioned transversely "with respect to the longitudinal axis of the neck 4.

Intermediate the length of the neck 4 and within the tub-e'is' a partition In which is provided with a central aperture II. The inner face of the screen portion 6 of the tube carries afluorescent coating [2 which in the operation of the tube is acted upon by the electron stream discharged from thegun l to cause the material constituting the layer l2 to-fluoresce and give off light. In this type-of tube, the electron gun I is so oriented that the electron stream is projected at an angle to the longitudinal axis of' thetube. As will be hereinaftermorefully described, this stream is subsequently deflected in such a manner as to project through the'aperture II.

The tube I hereinbeiore'describe'd is conventional and'per se'consti'tutes no part ofthe present invention. However, my invention is applicable to a tube of this type, such tubes being commonly used for television reception.

It is known that electrons in motion can be deflected during passage through a magnetic field. It is also known that in the usual cathode-ray tube, the motion of the electrons discharged from the gun I gives rise to ions. The tube I is evacuated but within the limits of efiiciency of present day vacuum pumps, a small trace of residual gas remains in the tube. In addition, occluded gases are contained in the walls of the tube. Consequently, during the passage of the electron stream, such gases are ionized. It is also known that the ions thus produced have a detrimental effect upon the fluorescent material I2 tending to de-activate such material or burn it.

It is further known that ions are also responsive 'to a magnetic field. However, for a magnetic field of predetermined intensity the electrons and ions are deflected a different degree. Consequently, the construction of tube I is such that it is to be used with a device for setting up magnetic fields in such fashion as to deflect the electron stream and ion stream at spaced points along the length of the streams. The angle of projection of the electron stream from the gun I is then so correlated with respect to the spaced magnetic field as to deflect the electron stream from its original path at an angle to the axis of the tube to a direction whereby the electron stream projects through the aperture II and impinges upon the material I2 carried upon the screen portion 6. In view of the fact that the ions do not respond to the deflecting force of the magnetic field to the same degree that do the electrons, it can readily be seen that a force couple correlated to bring the electron stream to a position whereby it will project through the aperture I I would not bring the ion stream into this coincident position. Consequently, the ions are prevented from emerging through the aperture I I and, hence, are prevented from impinging upon the layer of fluorescent material I2.

My invention is particularly directed to the setting up of magnetic fields within a conven' tional cathode-ray tube I and comprises essentially a pair of bar magnets I3 and I4. The magnets I3 and I4 are conveniently constructed of rectangular cross section. However, said magnets may be of any desired section. The magnets I3 and I4 are carried upon a ring I 5 which is a nonmagnetic material preferably a metal such as aluminum, copper, brass or the like. The magnets I3 and I4 are secured upon the outer face of the ring I5 and are diametrically positioned with respect to each other. To secure the magnets to the ring a strap I6 embraces an intermediate portion of each magnet, said strap being substantially U-shaped and having its ends passed through apertures in the wall of the ring and bent at the interior of the ring as shown best at I! in Fig. 5. The straps I6 are preferably constructed of metal preferably of the non-magnetic type.

Within thering I5 a pair of diametrically opposite disposed cantilever springs I8 are positioned, said springs being secured by means of rivets I9 to the ring I5. The arrangement is such that the ring I5 may be telescopically positioned over the neck 4 of the cathode-ray tube, the arms of the springs I8 embracing the walls of the tube and holding the ring I5 in place upon the tube.

The ring I5 is circular and is adapted to carry 1 a plate which is provided with a circular aperture slightly larger in diameter than the outer diameter of the ring I5, the arrangement being such that plate 26 may be rotated upon the outer surface of the ring I5 for a purpose to be hereinafter more fully described. The plate 20 has a substantially oval periphery and is thicker radially along the major axis of the oval than it is along its minor axis as indicated at 2i and 22 respectively in Fig. 5. The plate 20 is constructed of a ferro-magnetic material and its face is adapted to make contact with the ends of the oppositely disposed magnets 53 and It. To prevent axial movement of the plat 20 upon the ring I5 struck-up lugs 23 may be formed upon the end of the tubular ring I5. Thus the plate 20 will be confined between the ends of the magnets I3 and I 4 and the struck-up lugs 23.

The assembly illustrated in Figs. 5 and 6 when mounted upon the neck l of the tube is so positioned thereon as to bring two corresponding ends of the magnets I3 and I4 immediately adjacent the projecting members or flags 9. The polarity of the magnet ends positioned adjacent the flags 9 is as indicated in Fig. 1, that is, the north pole of one magnet is disposed diametrically opposite from the south pole of the other magnet. The opposite ends of the magnets, namely, those ends which are in contact with the plate 20 are positioned toward the screen-end of the tube.

When the assembly is thus mounted upon the neck of the tube I two magnetic fields are established across the neck of the tube, said fields being spaced from each other axially along the neck of the tube and by virtue of the disposition of the magnets the fields are of opposite direction. The plate 2G by virtue of the fact that it is constructed oi a ferro-magnetic material and is in contact with the respective ends of the magnets I3 and It functions to provide a low reluctance path between these ends of the mag nets. Consequently, the magnetic field established directly between these ends of the magnets is relatively reduced in intensity with respect to the field established between the opposite ends of the magnets.

It will be noted that the magnetic paths provided by the plate 20 are of minimum cross section adjacent the minor axis of the oval. The strength of the magnets I3 and M is such with respect to the cross sectional area of the plate at its narrowest portions that the plate is saturated under all conditions of operation. In this regard my present device partakes of the advantages of the invention described in my copending application, hereinbefore identified.

When the magnet assembly has been mounted upon the neck of the tube i, those poles of the two magnets which contact the plate 23 are disposed toward the screen-end of the tube and the opposite poles are disposed toward the baseend of the tube, the latter poles being disposed in radial alignment with the flags 9. Two spaced magnetic fields are thus provided which extend diametrically across the neck of the tube. By virtue of the fact that the low reluctance path established by the plate 28] connects the two poles adjacent the screen end of the tube, the strength of the field which extends diametrically across the tube directly between the two poles will be weaker than the strength of the field which eX- tends between the two poles adjacent the baseend of the tube.

When the tube is connected in its proper circuit and the element l functions to discharge a stream of electrons, said electron stream ini tially will be discharged at an angle to the longitudinal axis of the tube as indicated at 2 3 in sensuous rF'ig; 2. "When thee-electron streanrv encounters the rma'gnetic afield established 'iby. the ends 'of ithe rmagnets adjacentlthel:baseaend ofithe. tube said selectron istream will be -abruptlyzchan'ged ainadi- -'rection*asindicatedat in Fig.2 2. ".Thestream of electrons hthenzproceeds along the i deflected line luntil it-zencounters the second. magnetic field the first deflection will be: greaterthan the degree of thefisecond deflection. .The magnetic fields-are. so correlated with respect to: strength nand areisospaced as to causerthe streamtof .elec- 'trons'aafter:beingideflectedI the second time to proceed substantially alongthe! longitudinal axis of the'itube and :befiprojected through the aperture l I in the wall [0.

In view of the fact that the tube i although evacuated rcontains residual quantities of gas, the moving stream of electrons gives rise to a stream of ions. These ions are also affected by the magetic fields but arenot affected to the I same degree as is the stream ofelectrons. Consequently, when the magnetic fields are so adjusted as to cause the stream of electrons to project through the aperture II, the ion stream will be so deflected as to impinge upon the-wall H). In this manner the ions.-arepreventedfrom passing through the aperture Hi and impinging upon the fluorescent surface I 2.

Ithasbeen found in the operation of the usual cathode-ray tube particularly for television uses thata-phenomena known as.shadow1is encountered. This phenomena exhibits itself in that a portion of the screen is devoid of illumination. The portion of the screen so effected usually occurs adjacent the periphery of the screen and it is frequently observed that the contour of the shadowed area is somewhat arcuate. Although it is not definitely known precisely what causes this effect it is believed that it is caused by a portion of the electron stream engaging a peripheral edge of the aperture H. In this manner a portion of said stream is obstructed. However, whatever the cause of shadow may be, I have found that by slightly displacing the second magnetic field, that is the one established toward the screen-end of the tube, the shadow may be elim inated.

I have found that when shadow occurs upon the screen of a fluorescent surface it can be eliminated by rotating the plate 20 from its normal position, that is, its position with its major axis in alignment with the two magnets I3 and I4. Under normal circumstances, that is, when the major axis of the plate 20 is coincident with the line connecting the magnets l3 and M the direction of the magnetic field is along the broken line 21 in Fig. 3. When the plate 20 is rotated from its normal position as indicated in Fig. 4 I have found that the direction of the magnetic field shifts as indicated by the broken line 28. It can be seen that the line of direction of the magnetic field is rotated about the center of curvature of the ring I5. I have also noted that the degree of rotation of the direction line of the magnetic field is slightly greater than the degree of rotation or displacement of the major axis of the plate 20 from its normal position.

In order to prevent overshifting of the plate 20, that is, the shifting of the plate beyond the points where its influence would have any effect "upon eliminating-shadow, the'plateimay be protitled with struck up projections 27' which function as stops when thesame abut against one of the magnet-ends.

By the' proper.manipulation of the plate 20, that is its" rotation ina-clockwise or counterclockwise direction I have found that shadow upon the tube .screenca'n'be eliminated. Inview of the fact that under normal operating conditions shadow is a constant which-appears to bee characteristic of the :tubeand: supplemental apparatus employed --w'ith the'tube, the proper adjustment of the plate "zu'toseliminate the-shadow when once made funcitionsto-correct the defect permanently. In other -words,'with' the 'magnetic'assembly mounted upon the neckof the-tube and the plate 20 properly adjusted the tube functions ina perfect manner solongas the adjustment of the magnetic assembly or the adjustment of the plate'Z D is not -altered.

I claim as my invention: lJA device for magnetically deflecting an electron-:beam in-a cathode-ray tube, comprising a ring constructed of non-magnetic rigid material,

apairef bar magnets carried upon said ring, said magnets'being disposed upon diametrically op posite sides of said *ringwith the poles of one :magnet disposed opposite unlike pole of the other magnet, means for remcvably mounting saidring 'upon the neck of a cathodeuay tube with the magnets disposed substantially parallel to the axis of said neck; andanendless plate of ferro-magnetic-material mounted upon saidring and circumscribing'thesame, said plate being in movable-contact with diametrically opposed ends of said rnagnets to providea relatively low reluctance path for magnetic flux circumscribing said ring.

2. A device for magnetically deflecting an electron beam in a cathode-ray tube, comprising a ring constructed of non-magnetic rigid material, a pair of bar magnets carried upon said ring, said magnets being disposed upon diametrically 0pposite sides of said ring with the poles of one magnet disposed opposite unlike poles of the other magnet, means for removably mounting said ring upon the neck of a cathode-ray tube with the magnets disposed substantially parallel to the axis of said neck, and an endless plate of ferromagnetic material mounted upon said ring and circumscribing the same, said plate being in contact with diametrically opposed ends of said magnets to provide a relatively low reluctance path for magnetic flux circumscribing said ring and portions of said plate intermediate said magnet ends being of restricted cross-section whereby said restricted portions are magnetically saturated by the magnetomotive force of said magnets.

3, A device for magnetically deflecting an electron beam in a cathode-ray tube, comprising a ring constructed of non-magnetic rigid material, a pair of bar magnets carried upon diametrically opposite sides of said ring with the poles of one magnet disposed opposite unlike poles of the other magnet, means for removably mounting said ring upon the neck of a cathode-ray tube with the magnets disposed substantially parallel to the axis of said neck, and an endless plate of ferro-magnetic material rotatably mounted upon said ring and circumscribing the same, said plate being in movable contact with diametrically opposed ends of said magnets to provide a relatively low reluctance path for magnetic flux circumscribing said ring, said plate being of varying cross-sectional area throughout its length.

4. A device for magnetically deflecting an electron beam in a cathode-ray tube, comprising a substantially circular cylindrical ring constructed of non-magnetic rigid material, a pair of bar magnets carried upon diametrically opposite sides of said ring with the poles of one magnet disposed opposite unlike poles of the other magnet and with the lengths of said bar magnets disposed substantially parallel to the axis of said cylindrical ring, means for mounting said ring in coaxial relationship with, and upon, the neck of a cathode-ray tube, an endless plate of ferro-magnetic material rotatably mounted upon said ring, said plate being provided with a substantially circular aperture for seating the plate upon the ring, said plate having a substantially oval periphery and the face of said plate being in slidable contact with opposite ends of the magnets whereby rotation of said plate displaces the axis of the magnetic field established between said opposed magnet ends.

5. A device for magnetically deflecting an electron beam in a cathode-ray tube, comprising a substantially circular cylindrical ring constructed of non-magnetic rigid material, a pair of bar magnets carried upon diametrically opposite sides of said ring with the poles of one magnet disposed opposite unlike poles of the other magnet and with the lengths of said bar magnets dis-posed substantially parallel to the axis of said cylindrical ring, means for mounting said ring in coaxial relationship with, and upon, the neck of a cathode-ray tube, an endless relatively fiat plate of ierro-magnetic material rotatably mounted upon said ring, said plate being provided with a substantially circular aperture for seating the plate upon the ring with its flat surfaces disposed transversely with respect to the ring surface, said plate having a substantially oval periphery and the face of said plate being in slidable contact with opposite ends of the magnets whereby rotation of said plate displaces the axis of the magnetic field established between said opposed magnet ends.

6. A device for magnetically deflecting an electron beam in a cathode-ray tube, which comprises in combination, a pair of bar magnets, means for holding said magnets in substantially parallel spaced relationship with opposite poles opposed to establish two spaced magnetic fields between the opposed magnet ends, a ferro-magnetic endless ring of non-uniform cross section rotatably carried upon said means and in movable contact with one pair of opposite ends of said magnets, and means for mounting said magnets and holding means upon the neck of a cathoderay tube.

MYRON R. HEPPNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,177,688 Cawein Oct. 31, 1939 2,200,039 Nicoll May 7, 1940 2,211,613 Bowie Aug. 13, 1940 2,258,643 De Gier et a1 Oct. 14, 1941 2,274,586 Bronson Feb. 24, 1942 2,460,609 Torsch Feb. 1, 1949 2,472,766 Woodbridge June 7, 1949

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